1. Field of the Invention
This invention relates to the solution mining of subterranean trona and/or nahcolite ore deposits with two solvents, aqueous sodium hydroxide and aqueous hydrogen chloride, that are generated electrodialytically.
2. Description of the Prior Art
The use of aqueous sodium hydroxide (NaOH) for solution mining of subterranean trona ore and nahcolite ore deposits is known. U.S. Pat. No. 3,184,287 issued to Gancy describes a cyclic process for solution mining trona with aqueous sodium hydroxide, this solvent being regenerated by causticization of aqueous sodium carbonate with lime. U.S. Pat. No. 3,953,073 issued to Kube describes the use of aqueous sodium hydroxide for solution mining of trona and nahcolite, and of other NaHCO.sub.3 -containing ores, and discloses that the solvent requirements may be met either by causticization of soda ash with hydrated lime or by the electrolytic conversion of sodium chloride to sodium hydroxide.
Aqueous sodium hydroxide that is produced by the electrolysis of aqueous sodium chloride brines also results in the coproduction of chlorine gas and hydrogen gas. Electrodialysis of such aqueous brines in a cell having permselective bipolar membranes, by contrast, allows aqueous sodium hydroxide to be produced without coproduction of chlorine and hydrogen.
U.S. Pat. No. 4,219,396 issued to Gancy et al. describes the operation of an electrodialysis cell in which soda ash is recovered using a brine feed. Aqueous sodium chloride is introduced as feed brine to salt zone of the electrodialysis cell, aqueous hydrogen chloride is removed from an acid zone, and NaOH-enriched aqueous sodium carbonate is withdrawn from a base zone and carbonated with CO.sub.2.
U.S. Pat. No. 4,391,680 issued to Mani et al. describes the operation of a two-compartment electrodialysis cell in which an aqueous brine feed is introduced into the first compartment. An acidified salt solution, containing HCl, is withdrawn from the first compartment for use as feed to an electrolytic cell, and aqueous sodium hydroxide is withdrawn from the second compartment.
The method of the present invention relies on the electrolytic production of two solvents that are utilized in the solution mining of subterranean ore deposits of trona or nahcolite. The invention employs aqueous sodium hydroxide as the primary solution mining solvent, while nevertheless avoiding the unwanted byproducts (like chlorine) that typically result from electrolytic production of sodium hydroxide, as well as avoiding the environmental drawbacks associated with the regeneration of lime in lime causticization (for producing NaOH).